Heretofore, it is known a sensor having attached thereto a detection element (sensor element) in the form of an axially extending plate and formed with a detection section at a front end side to face an object to be measured. Enumerated as such a sensor are a gas sensor such as a λ (lambda) sensor, a wide-range air/fuel ratio sensor, oxygen sensor and NOx sensor, and a temperature sensor for detection of temperature.
The plate-shaped detection element is generally configured so as to have a detection section at an axial (longitudinal) front end side and electrode terminal sections at both side surfaces at a rear end side. A sensor that is regarded as one having such a detection element is configured to electrically connect a lead frame (metallic terminal member) made of an electrically conductive material to an electrode terminal section for thereby forming a portion of an electric current path for conduction of electrical current between the detection element and an external device by means of the lead frame. In the meantime, electrical currents such as detection current (detection signal) according to a result of detection by the detection element and electrical current for power supply to a heater in case the detection element has the heater flow through the electrical current path electrically connecting the detection element and the external device.
As a sensor having a lead frame is known a sensor configured to use a lead frame having a resilient contact portion that serves as a resiliently deformable leaf spring and hold a detection element within an insertion hole of a separator, with the resilient contact portion of the lead frame being in a condition of being brought into contact with the resilient contact portion of the lead frame (refer to Patent Document 1). In the meantime, the resilient contact portion is provided to the lead frame so as to be in a condition of being connected at one of opposite ends to a lead frame main body section (in a one-point support condition).
In case of a sensor with such a structure, it becomes possible to make good the connection condition between the lead frame and the electrode terminal section of the detection element by using a lead frame configured so that a resilient contact portion exerts a large resilient force. In the meantime, as a lead frame with a resilient contact portion exerting a large resilient force are enumerated, for example, a lead frame formed so as to be large in the width size, a lead frame formed so as to be large in the thickness, etc.
Patent Document 1: Unexamined Japanese Patent Publication No. 2001-188060.
However, in case a lead frame having a resilient contact portion that exerts an excessively large resilient force is used as in a prior art sensor, a large pressure more than needed is applied from the lead frame to the detection element at the time of assembly of the lead frame and the detection element, so that a damage of the detection element such as chipping or breakage may possibly be caused by that pressure.
Further, since a lead frame large in the width size requires a wide space for disposition thereof, there arises a problem that such a lead frame is not suited for use in a sensor that is needed to be small-sized. Further, in the event a lead frame large in the width size is used for a detection element formed with a plurality of electrode terminal sections that are small in the width size and positioned close to each other, there is a possibility that one lead frame is brought into contact with all the plurality of electrode terminal sections and a suitable electrical current path cannot be formed.
In the meantime, by using a lead frame that is formed small in the width side for such a detection element having a plurality of electrode terminal sections, the current path can be formed. However, a lead frame having a resilient contact portion in a one-point support condition as the above-described prior art lead frame tends to lack a resilient force if formed smaller in the width size, thus being incapable of sufficiently contacting the electrode terminal section due to the lack of resiliency and possibly causing the condition of connection with the electrode terminal section to be unstable.